Solar-thermal reaction processing

ABSTRACT

In an embodiment, a method of conducting a high temperature chemical reaction that produces hydrogen or synthesis gas is described. The high temperature chemical reaction is conducted in a reactor having at least two reactor shells, including an inner shell and an outer shell. Heat absorbing particles are included in a gas stream flowing in the inner shell. The reactor is heated at least in part by a source of concentrated sunlight. The inner shell is heated by the concentrated sunlight. The inner shell re-radiates from the inner wall and heats the heat absorbing particles in the gas stream flowing through the inner shell, and heat transfers from the heat absorbing particles to the first gas stream, thereby heating the reactants in the gas stream to a sufficiently high temperature so that the first gas stream undergoes the desired reaction(s), thereby producing hydrogen or synthesis gas in the gas stream.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/383,875, filed Mar. 7, 2003 and now U.S. Pat. No. 7,033,570, whichclaims the benefit of U.S. Provisional Application No. 60/362,563, filedMar. 7, 2002, is a continuation-in-part of U.S. application Ser. No.11/282,116, filed Nov. 17, 2005, which claims the benefit of andincorporates in by reference U.S. application Ser. No. 10/383,875, filedMar. 7, 2003 and now U.S. Pat. No. 7,033,570, and that claims thebenefit of U.S. Provisional Application No. 60/628,641, filed Nov. 17,2004, and is a continuation-in-part of U.S. application Ser. No.10/239,706, filed Feb. 24, 2003 now U.S. Pat. No. 6,872,378, which isthe national stage of PCT Application Number PCT/US01/15160, filed May8, 2001, which claims the benefit of U.S. Provisional Application No.60/203,186, filed May 8, 2000, all of which are hereby incorporated byreference to the extent not inconsistent with the disclosure herein.

ACKNOWLEDGEMENT OF GOVERNMENT SUPPORT

This invention was made, at least in part, with funding from the UnitedStates Department of Energy under grant numbers DE-FC36-99GO10454 andDE-AC36-99GO10337. The United States Government has certain rights inthis invention.

FIELD

In general, the disclosure relates to solar-thermal reactors andprocesses for carrying out high temperature chemical reactions. Moreparticularly in an embodiment, it relates to a rapid-heating, shortresidence time solar-thermal process for carrying out highly endothermicdissociation reactions to produce hydrogen or hydrogen containing gases.Most particularly, in an embodiment it relates to those dissociationreactions wherein a solid particulate material is produced by thedissociation of a gaseous precursor.

BACKGROUND

There is a significant interest to develop benign processes forproducing hydrogen that can be used as a fuel to power fuel cellvehicles. Such processes should reduce the amount of greenhouse gasesproduced, thus, minimizing impact on the environment. However, currentmethods for producing hydrogen incur a large environmental liability,because fossil fuels are burned to supply the energy to reform naturalgas (primarily methane, CH4) to produce hydrogen (H2).

High temperatures above approximately 1500 K are required for producinghydrogen and carbon black at high rates by the direct thermaldissociation of methane [CH4+heat-->C+2H2] (reaction 1), ethane[C2H6+heat→2C+3H2] (reaction 2), propane [C3H8+heat-->3C+4H2] (reaction3), or, in general, a mixture of gases such as natural gas genericallyrepresented as CxHy [CxHy+heat-->xC+(y/2)H2] (reaction 4).

Hydrogen can also be produced by the dry reforming of methane withcarbon dioxide [CH4+CO2-->2CO+2 H2]. It is also possible to carry outdissociation of methane simultaneously with the dry reforming of methaneif excess methane is present relative to that required to react carbondioxide. Such processes are useful since they can provide for a highhydrogen content synthesis gas by utilizing natural gas from natural gaswells that contain a high concentration of carbon dioxide (typically 10to 20 volume % CO2) or using landfill biogas (30 to 40 volume % CO2).

Hydrogen can also be produced by the thermal dissociation of hydrogensulfide [H2S+heat-->H2+S] (reaction 5).

For these types of dissociation reactions, a solid (either C or S) isformed as a co-product (with H2) of the reaction. Often, the solid thatis formed is in the state of fine particles. These particles have atendency to deposit along the walls of reaction vessels or coolingchambers where the dissociation is occurring. If deposition occurs alongthe inside walls of the heated reactor, the particles tend to aggregateand crystallize. For the case of carbon deposition, the normallyamorphous ultra-fine particles will grow in size and graphitize. Largegraphitic carbon particles are less reactive compared to more amorphousfine sized particles and, hence, are of lower value. Furthermore,deposition on the reactor walls can cause plugging of the reactor andeventual shutdown of the process, thus, preventing continuous operation.In addition, carbon deposition on an outer transparent wall of a solarreactor can lead to overheating of the reactor wall.

U.S. Pat. No. 4,552,741, to Buck et al., reports carbon dioxidereforming of methane in a system comprising two catalytic reactors. Oneof the catalytic reactors is heatable with solar energy. In theabstract, the reactors are stated to be “filled with a catalyst”.

U.S. Pat. No. 5,647,877 reports solar energy gasification of solidcarbonaceous material in a liquid dispersion. The solid carbonaceousmaterial is heated by solar energy and transfers heat to a surroundingliquid. Hydrogen is produced in the process by thedecomposition/gasification of the hydrocarbon (coal) particles.

EP 0675075A reports the use of solar energy to generate hydrogen fromwater. In the reported process, water is reduced to hydrogen with ametal, followed by reduction of the metal oxide with a reducing agent.

Hence, there is a need to develop high temperature environmentallybenign processes for the production of H2 by thermal dissociation ofhydrocarbon gases, such as natural gas, and to prevent the deposition ofthe products of dissociation on reactor walls.

SUMMARY

Various methods and apparatus are described for a high temperaturechemical reactor. In an embodiment, a high temperature chemical reactorconducts a reaction process to that produces hydrogen or synthesis gas.The reactor may have at least two reactor shells, including an innershell and an outer shell. The inner shell has an inlet and an outlet andthe outer shell is nonporous and substantially encloses the second innershell. A particle inlet provides heat absorbing particles in a first gasstream flowing in the inner shell. The reactor is heated at least inpart by a source of concentrated sunlight. The inner shell is heated bythe concentrated sunlight, and the inner shell re-radiates from theinner wall and heats the heat absorbing particles in the first gasstream flowing through the inner shell, and heat transfers from the heatabsorbing particles to the first gas stream. The heat absorbingparticles heats the reactants in the first gas stream to a sufficientlyhigh temperature so that the first gas stream undergoes the desiredreaction(s), thereby producing hydrogen or synthesis gas in the firstgas stream.

BRIEF DESCRIPTION OF THE DRAWINGS

The multiple drawings refer to the embodiments of the invention.

FIG. 1 is a cross-sectional view of the central portion of asolar-thermally heated fluid-wall reactor having three walls. Theinnermost wall of the reactor is a porous “reactor” wall, the nextoutermost wall of the reactor is a solid “heating” wall, and theoutermost wall of the reactor is a transparent “protection wall”.

FIG. 2 is an overall cross-section of another reactor of the disclosure.

FIG. 3 is a cross-section of a reactor having a transparent window inthe outer shell.

FIG. 4 is a schematic of a solar-thermal natural gas dissociation systememploying a solar thermally heated fluid-wall reactor of the disclosure.

While the invention is subject to various modifications and alternativeforms, specific embodiments thereof have been shown by way of example inthe drawings and will herein be described in detail. The inventionshould be understood to not be limited to the particular formsdisclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention.

DETAILED DISCUSSION

In an embodiment, a high temperature chemical reactor conducts areaction process to that produces hydrogen or synthesis gas. The reactormay have at least two reactor shells, including an inner shell and anouter shell. The inner shell has an inlet and an outlet and the outershell is nonporous and substantially encloses the second inner shell. Aparticle inlet provides heat absorbing particles in a first gas streamflowing in the inner shell. The reactor is heated at least in part by asource of concentrated sunlight. The inner shell is heated by theconcentrated sunlight, and the inner shell re-radiates from the innerwall and heats the heat absorbing particles in the first gas streamflowing through the inner shell, and heat transfers from the heatabsorbing particles to the first gas stream. The heat absorbingparticles heats the reactants in the first gas stream to a sufficientlyhigh temperature so that the first gas stream undergoes the desiredreaction(s), thereby producing hydrogen or synthesis gas in the firstgas stream. A solar concentrator designed to optimize an amount of solarthermal heating for the reaction process by using concentrated sunlightto transfer heat at extremely high rates by radiation heat transfer fromthe inner shell. The length of the inner shell and amount of fluxprovided by the solar concentrator are designed to carry out hightemperature thermal dissociation reactions requiring rapid-heating andshort residence times using solar energy

The disclosure provides a method for carrying out high temperaturethermal dissociation reactions requiring rapid-heating and shortresidence times using solar energy. In particular, the method of thedisclosure allows production of hydrogen and hydrogen containing gasesthrough thermal dissociation of a gas comprising hydrocarbon gases ormixtures thereof (such as natural gas) and/or hydrogen sulfide. Themethods of the disclosure also allow production of hydrogen through dryreforming of methane with carbon dioxide. The disclosure also provideshigh temperature solar reactors.

In particular, the disclosure provides a high temperature solar-thermalreactor comprising

a. a first inner shell which is at least partially porous, the firstinner shell having an inlet and an outlet;

b. a second inner shell which is nonporous and which substantiallyencloses the first inner shell;

c. a first gas plenum located substantially between the first and secondinner shell, the first plenum having an inlet and an outlet, wherein thefirst plenum outlet is formed by the pores of the first inner shell;

d. an outer shell which is nonporous, at least partially transparent,and which substantially encloses the second inner shell; and

e. a second gas plenum located substantially between the second innershell and the outer shell, the second plenum having an inlet and anoutlet,

wherein the reactor is heated at least in part by a source ofconcentrated sunlight and the first inner shell is prevented from fluidcommunication with the first and second gas plenums inside the reactor,except for fluid communication between the first inner shell and thefirst gas plenum through the pores of the first inner shell.

FIG. 1 is a cross-section of the central portion of a reactor in thepresent disclosure. In the figures, the same numbers are used toidentify like features. In the configuration shown in FIG. 1, thereactor (1) has a first, innermost, inner shell (3) which is at leastpartially porous, a second inner shell (5) which is non-porous, and anouter shell (7) which is at least partially transparent to solarradiation and is also non-porous. As used herein, “shells” encompasstubes, pipes or chambers which are elongated along a longitudinal axis.As used herein, a “porous” shell region permits gas flow through thewalls of the region while a “nonporous” shell region does not. In areactor with three shell, the first inner shell is substantiallyenclosed by the second inner shell and the outer shell and the secondinner shell is substantially enclosed by the outer shell. As usedherein, “substantially encloses” means that one shell is enclosed byanother for most of the length of the shell. The ends of a shell that issubstantially enclosed by another may extend past the ends of the othershell (e.g. the ends of the first inner shell may extend past the endsof the second inner shell and/or the outer shell). FIG. 1 illustrates anembodiment where the “shells” are concentric tubes of circularcross-section.

FIG. 1 also illustrates the central portion of the first (41) and second(43) gas plenums. During operation of the reactor, gases are flowedthrough the first inner shell and the two gas plenums by connecting eachof the respective inlets to at least one gas source. The porousregion(s) of the first inner shell serve as an outlet to the first gasplenum. FIG. 1 illustrates three gas streams, a first gas stream (21)flowing through the first inner shell, a second gas stream (23) flowingthrough the first plenum, and a third gas stream (25) flowing throughthe second plenum. Preferably, the first gas stream is prevented frommixing with the third gas stream within the reactor and mixing betweenthe first and second streams is limited to mixing within the first innershell due to flow of gas from the second gas stream through the porousregion(s) of the first inner shell. In other words, the first innershell is preferably prevented from fluid communication with the firstand second plenum inside the reactor, except for fluid communicationbetween the first inner shell and the first plenum through the porousregion(s) of the first inner shell. In addition, during operation of thereactor fluid communication between the first inner shell and the firstplenum is primarily in the direction from the first plenum to the firstinner shell. The pressure within the first plenum is high enough toovercome the resistance of the porous first inner shell and still have apressure (at the instant the gas from the second gas stream leaves thepore) greater than the pressure inside the shell. Restricting fluidcommunication between the first inner shell and the first and secondplenum can prevent deposition of particulate reaction products on theother shells and reduce the amount of gas from the second and third gasstreams which enters the first inner shell. The overall volumetric flowrate of gases through the first inner shell can affect the residencetime and the production throughput of the reactor. If the second andthird gas streams are different, it is also preferred to prevent mixingof the second and third gas streams within the reactor.

In one embodiment, mixing of the gas streams is restricted by seals. Ifthe inner and outer shells are tubes as shown in FIG. 1, the plenums arefurther defined by these seals, since they serve to define the gasvolume. Statement that a plenum is located “substantially between” twoshells encompasses an extension of the plenum beyond the two shells intoa sealing structure. In addition, a plenum being “substantially located”between two shells encompasses reactor configurations where otherreactor elements, for example thermal insulation, are also locatedbetween the two shells. FIG. 2 illustrates one sealing configurationwhich can be used to prevent mixing of the gas streams within thereactor. In FIG. 2, the inlet and outlets for the inner and outer shellsare illustrated as part of the sealing structures (31) and (33). Theinner shell inlet (11) and outlet (12) are substantially sealed from thefirst plenum (41) and second plenum (43). FIG. 2 also shows the firstplenum inlet (13), with the outlet of the first plenum being the porousregion of the inner shell, and second plenum inlet (15) and outlet (16).The sealing structures shown in FIG. 2 are cooled with water (34) toprevent heat damage to the fitting and sealing materials. Other suitableseal configurations are known to those skilled in the art. Furthermore,the seal configuration may be different at the inlet and outlet ends ofthe reactor.

The reactor shown in FIG. 1 is operated generally as follows.Concentrated solar-thermal radiation (91) passes through the outer“protection” shell (7) and directly heats the second inner “heating”shell (5). The nonporous heating shell re-radiates from its inner walland heats the first inner “reaction” shell (3). Hence, the inner“reaction” shell (3) is heated indirectly by concentrated sunlight fromthe surrounding “heating” shell (5). The inner “reaction” shell (3)re-radiates from the inner wall and heats the radiation absorberparticles (27) and first gas stream (21) flowing through it. Whenheated, the first gas stream undergoes the desired reaction(s). As thefirst gas stream is heated and the desired reaction(s) occur, one ormore product gases are added to the gas stream. A second gas stream (23)of non-oxidizing and non-dissociating “fluid-wall” gas flows in theannular region between the central “heating” shell and the inner“reaction” shell. The “fluid-wall” gas enters the first plenum betweenthe inner and outer shell through an inlet and exits the plenum throughan outlet. One outlet of the first plenum is the porous section of theinner shell. An additional outlet for the first plenum may be used, solong as sufficient gas flow is provided through the porous section ofthe inner shell. The “fluid-wall” gas flows through the pores of theporous section of the “reaction” shell (3), exits radially along theinside of the “reaction” shell and provides for an inner “fluid-wall”gas blanket (29) that prevents deposition of dissociation productparticles on the inside wall of the “reaction” shell. After entering thefirst inner shell, the “fluid-wall” gas exits through the outlet of thefirst inner shell. A third gas stream (25) of non-oxidizing andnon-dissociating “purge” gas flows in the annular region between theouter “protection” shell and the center “heating” shell, thus preventingoxidation of the central “heating” shell and any insulation that may bepresent between the “protection” and “heating” shell.

In another embodiment, the reactor comprises

a) an inner shell which is at least partially porous, the inner shellhaving an inlet and an outlet;

b) an outer shell which is nonporous, at least partially transparent,and which substantially encloses the second inner shell; and

c) a gas plenum located substantially between the inner and outer shell,the plenum having an inlet and an outlet,

wherein the reactor is heated at least in part by a source ofconcentrated sunlight and the only fluid communication between the innershell and the gas plenum inside the reactor occurs through the pores ofthe inner shell.

This reactor is operated as follows. Concentrated solar-thermalradiation passes through the outer “protection” shell and directly heatsthe inner “reaction” shell. The inner “reaction” shell re-radiates fromthe inner wall and heats the radiation absorber particles and first gasstream flowing through it. When heated, the first gas stream undergoesthe desired reaction(s). A second gas stream of non-oxidizing andnon-dissociating “fluid-wall” gas flows in the annular region betweenthe outer “protection” shell and the inner “reaction” shell. The“fluid-wall” gas enters the plenum between the inner and outer shellthrough an inlet and exits the plenum through an outlet. The poroussection of the inner shell forms one outlet of the plenum. An additionaloutlet for the plenum may be used, so long as sufficient gas flow isprovided through the porous section of the inner shell. The “fluid wall”gas flows through the pores of the porous section of the “reaction”shell, exits radially along the inside of the “reaction” shell andprovides for an inner “fluid-wall” gas blanket that prevents depositionof dissociation product particles on the inside wall of the “reaction”shell.

In general, the shells comprising the reactors of the disclosure may bepositioned vertically or horizontally, or in any other spatialorientation. For the case of a vertical reaction shell process, theapparatus may be arranged to provide upward or downward flow of the gasstream and the cloud of particles. Upward flow guarantees thataggregated particles will not be carried through the reaction shell.Downward flow reduces the potential for plugging in the solids feedline, if present. Preferably, the reactor shell is positioned verticallyand flow is downward.

The disclosure provides a method for carrying out a high temperaturechemical reaction process to produce hydrogen or synthesis gascomprising the steps of:

a) providing a reactor comprising at least two reactor shells, includingan innermost and an outer shell, wherein the innermost shell issubstantially enclosed by each of the other reactor shells, has an inletand an outlet and is at least partially porous and the outer shell isnonporous and at least partially transparent;

b) flowing a first gas stream comprising at least one reactant gas fromthe inlet to the outlet of the innermost shell;

c) flowing a second gas stream comprising a non-dissociating gasinwardly through the pores of the first inner shell;

d) providing heat absorbing particles in the first gas stream;

e) heating the heat absorbing particles at least in part with a sourceof concentrated sunlight through indirect solar thermal heating; and

f) transferring heat from the particles to the first gas stream, therebyheating the reactant gas to a sufficiently high temperature so that adesired amount of conversion of the reactant gas occurs, therebyproducing hydrogen or synthesis gas.

For a reactor having a first inner shell, a second inner shell, and anouter shell, the disclosure provides a method comprising the steps of:

a) providing a reactor comprising a first inner shell which is at leastpartially porous and has a first inner shell inlet and outlet, a secondinner shell which is nonporous and substantially encloses the firstinner shell, an outer shell which is nonporous, at least partiallytransparent and substantially encloses the second inner shell, a firstplenum substantially located between the first inner shell and thesecond inner shell and having a first plenum inlet and outlet, and asecond plenum substantially located between the second inner shell andthe outer shell and having a second plenum inlet and outlet wherein thefirst plenum outlet is formed by the pores of the first inner shell andthe first inner shell is prevented from fluid communication with thefirst and second gas plenums inside the reactor, except for fluidcommunication between the first inner shell and the first gas plenumthrough the pores of the first inner shell;

b) flowing a first gas stream comprising at least one reactant gas fromthe inlet to the outlet of the first inner shell;

c) flowing a second gas stream comprising a non-dissociating gas throughthe inlet of the first plenum, thereby causing part of the second gasstream to flow inwardly through the pores of the first inner shell;

d) flowing a third gas stream comprising a non-dissociating,non-oxidizing gas from the inlet to the outlet of the second plenum;

d) providing heat absorbing particles in the first gas stream;

e) heating the heat absorbing particles at least in part with a sourceof concentrated sunlight through indirect solar thermal heating; and

g) transferring heat from the particles to the first gas stream, therebyheating the reactant gas to a sufficiently high temperature so that adesired amount of conversion of the reactant gas occurs, therebyproducing hydrogen or synthesis gas.

The innermost inner shell (the first inner shell in a three-shellreactor) has an inlet and an outlet for the first gas stream. Theinterior of the innermost shell defines a reaction chamber within whichthe high temperature reaction takes place. The innermost shell iscapable of emitting sufficient radiant energy to raise the temperatureof the reactant gas(es) within the reaction chamber to a level requiredto initiate and sustain the desired chemical reaction. The innermostshell is made of a high temperature refractory material. The refractorymaterial subsequently heats flowing radiation absorber particles flowingthrough the first inner shell and is substantially chemically unreactivewith the particles or the reactant or product gases. A preferredmaterial for the innermost shell is graphite.

The innermost shell is at least partially porous. The innermost shellmay be wholly of porous material or may comprise one or more regions ofporous material. For example, the innermost shell may take the form of agraphite tube having a central porous region with nonporous ends. Theporous region(s) of the innermost shell are selected so that sufficientuniform flow of non-dissociating gas occurs radially inward through thepores to provide a fluid-wall protective blanket for the radially inwardsurface of the innermost shell. The fluid-wall can prevent particledeposition on the radially inward surface of the innermost shell. Theporosity of the porous region(s) can be varied and is selected on thebasis of the required gas flow and allowable pressure drop to providefor a fluid-wall of gas to prevent deposition along the inside wall ofthe reactor. The length of the porous section(s) of the “reaction” shellcan be varied and is determined by the zone where particle deposition ismost likely to occur. Likewise, the placement of the porous sectionalong the length of the “reaction” shell is determined by the mostlikely location of particle deposition. Preferably, the length of theporous section of the “reaction” shell is limited to where it is neededto prevent wall deposition of dissociation product particles. Too largeof a porous section will provide for too much fluid-wall gas enteringthe interior of the innermost “reaction” shell. The entry of fluid-wallgas into the “reaction” shell increases the overall volumetric flow rateof gases through the “reaction” shell, thus reducing residence time andlimiting the production throughput of the reactor.

A second inner shell substantially enclosing the first inner shell maybe present, but is not required. If no second inner shell is present the“reaction” shell is heated directly by concentrated sunlight passingthrough the “protection” shell and “fluid wall” gas is flowed in theplenum substantially located between the “reaction” shell and the“protection” shell.

The use of a second inner shell offers several advantages. The use of anonporous second inner shell distances the “fluid wall” gas from theouter “protection” shell, which can increase the safety of the processwhen the “fluid wall” gas is a flammable gas such as hydrogen.Furthermore, if the second inner shell is a tube made of a material suchas graphite, an electrical current can be run from one end of the tubeto the other and generate additional heat for the process throughresistance heating of the tube. This additional heat can supplement theprocess at times when the source of concentrated sunlight does notprovide the desired amount of energy (e.g. a cloudy day).

Typically, the second inner shell is composed of nonporous hightemperature refractory material. The second inner shell is mostpreferably made of solid graphite. As previously discussed, the secondinner shell can function as a “heating” shell, since it radiates heat tothe innermost shell. In addition, the combination of the first and thesecond inner shell at least partially defines a first plenum or volumefor the non-dissociating fluid wall gas.

Additional inner shells can be used in the process. If used, they aresized and positioned so that the innermost shell is enclosed by each ofthe other reactor shells (i.e. the reactor shells are substantially“nested” one inside the other). If additional inner shells are used,“purge” gas can be used to prevent oxidation of these shells as well.

The outer “protection” shell is at least in part transparent orsemi-transparent to the concentrated sunlight, thereby allowingconcentrated sunlight to flow through and heat the inner shell(s) of thereactor. The “protection” shell is made of a high temperature materialthat is oxidation resistant. A suitable material for the transparentportion of the outer shell is quartz. The transparent portion of theouter shell may be a transparent section, window or opening to allow theconcentrated sunlight into the vessel. The shell wall transparent area,allowing for concentrated sunlight entry and subsequent solar thermalheating, should be selected to provide heating during the desiredreaction residence time requirements for the process.

The outer shell may be made entirely of quartz. In this case, thesections of the internal wall of the outer shell where sunlight is notbeing concentrated and entering the vessel, may be coated with areflective material, such as silver, to keep the concentrated sunlightinside the reactor. If such a reflective coating is used, there must bean uncoated transparent section, window or opening to allow theconcentrated sunlight into the vessel.

Alternatively, the outer “protection” shell may be made of a refractorynon-transparent material with a section containing a transparent windowwhere concentrated sunlight can enter, as schematically illustrated inFIG. 3. In the configuration shown in FIG. 3, both a first (3) and asecond inner shell (5) are substantially enclosed by the outer shell.The “heating” shell (5) is directly exposed to concentrated sunlight inthe section of the shell located in the path of the sun through thetransparent section (9) of the “protection” shell (7). As shown in FIG.3, the “heating” shell may be surrounded by refractory insulation (6) inthe region where it is not directly exposed to concentrated sunlight viathe transparent section. The insulation may be concentrically placed andextends substantially from the “heating” shell to the concentric“protection” shell, although it may not completely fill the spacebetween the heating shell and the protection shell. The refractoryinsulation can be a combination of graphite insulation near the“heating” shell and an alumina type refractory insulation near the“protection” shell. This design arrangement allows concentrated sunlightto enter through a transparent section and heat the “heating” shellwhile the surrounding insulation reduces losses of ultraviolet radiationfrom the “heating” shell, thereby increasing the efficiency of theprocess. It is also possible to provide cooling of the outer metalrefractory “protection” shell, particularly in the region immediatelysurrounding the transparent window allowing concentrated sunlight todirectly heat the “heating” shell. The non-transparent refractorymaterial may be a metal with a sufficiently high melting point, such assteel. In FIG. 3, the inlet (11) to the first inner shell is shown ashaving a feed gas inlet (18) and optional heat absorbing particle feedinlet (19). The particle feed inlet is not required if the heatabsorbing particles are wholly generated by the dissociation process.

The combination of the outermost inner shell and the outer shell atleast partially defines a plenum or volume for gas. If no second innershell is used in the reactor, non-dissociating fluid wall gas flows inthe space between the outer shell and the inner shell. Otherwise, anon-oxidizing and non-dissociating “purge” gas typically flows between asecond plenum substantially located between the outer shell and thesecond inner shell to protect the second inner “heating” shell fromoxidation.

The first gas stream initially comprises at least one reactant selectedfrom CH4, C2H6, C3H8, generally CxHy, H2S, natural gas, or a combinationthereof. The first gas stream may contain substantial amounts of carbondioxide, as may be present in “biogases” such as landfill gas. Landfillgases may contain as much as 40% carbon dioxide. The first gas streammay also initially comprise a non-reactive gaseous component. Forexample, in lab-scale tests, methane is sometimes diluted with argon forsafety reasons. As the gas stream is heated and the reaction orreactions occur, one or more product gases are added to the gas stream.These product gases comprise H2 and, depending on the composition of thereactant gases, may also comprise incomplete dissociation products suchas C2H2, C2H4, or other gases. In the case of reactions (1 to 4),additional carbon particles are also produced, and in the case ofreaction (5), elemental sulfur is produced. A preferred reactant gasstream is natural gas or one containing natural gas. A most preferablereactant gas stream is natural gas which is free of mercaptans andhydrogen sulfide.

In the method of the disclosure, the first gas stream is heated to asufficiently high temperature within the reactor that the desired amountof conversion of the reactant gas(es) is obtained. Hydrogen formationmay take place below this temperature. Preferably the first gas streamis heated to at least about 1500 K within the reactor. As used herein,the use of “about” with reference to a temperature implies that thetemperature is within 25 K of the stated temperature. In otherembodiments, the reactant gas is heated to about 2100 K or heated to amaximum temperature in the range between about 1500 K and about 2700 Kor between about 1800 K and about 2400 K. The temperature inside theinnermost shell of the reactor can be measured with a thermocouple.Alternatively, temperatures inside the reactor can be measured with anoptical pyrometer. For a three-shell reactor, the hot zone temperaturemeasured with an optical pyrometer is typically the temperature of thenonporous “heating” shell, since the “heating” shell encloses the“reaction” shell in the hot zone. The temperature inside the inner“reaction” shell may be less than that of the “heating” shell due tothermal losses due to heating the porous shell and the gases in thefirst plenum and the reaction shell.

The reactors and methods of the disclosure allow conversion of at leastabout 30% of a hydrocarbon or hydrogen sulfide reactant gas. As usedherein, the amount of conversion is the ratio of the moles of reactantgas reacted to the moles of reactant gas supplied. In variousembodiments, the reactors and methods of the disclosure can produce atleast 50% or at least 70% conversion of reactant gas.

As used herein, the “residence time” is the time that the reactantgas(es) spend in the hot zone of the innermost “reaction” shell The hotzone length may be estimated as the length of the reactor directlyirradiated by the source of concentrated sunlight. The residence timedepends on the flow rate of the first gas stream containing the reactantgas(es), the flow rate of the fluid wall gas through the pores of theinner shell, the reactant gas temperature and the degree of conversionof the reactant gas(es). The residence time may be calculated throughmodeling or estimated by averaging the residence times of the componentsof the gas stream flowing through the innermost tube at reactiontemperature and assuming that half of the actual conversion occurs overthe entire length of the hot zone and contributes to the formation ofadditional moles of gas (e.g., 2 moles of hydrogen are formed for everymole of methane converted). In the methods of the disclosure, theresidence time is preferably between about 1 and about 50 milliseconds.More preferably, the residence time is between about 5 and about 30 ms.Most preferably, the residence time is between about 10 and about 20 ms.

In the methods of the disclosure, heat absorbing particles are providedin the first gas stream. The radiation absorbing particles are heatedindirectly by solar-thermal heating, and they must be easily separatedfrom the gas after processing. Typically, these radiation-absorbingparticles are carbon black. As used herein, “indirect” heating meansthat the heating is by radiation from a heated wall that is itselfheated indirectly or directly by solar-radiation. In one embodiment, theparticles are fine carbon black particles. Carbon black is chemicallystable at extremely high temperatures and can be easily separated fromthe flowing process gas using a filter and/or cyclone separator. Becausecarbon is produced according to hydrocarbon dissociation reactions, itis compatible with the hydrocarbon dissociation type of reactions to becarried out in the process for producing H2. Preferably, the particlescomprise recycled carbon black synthesized according to the dissociationreactions of the present disclosure. More preferably, the particles arecarbon black particles generated in-situ from the dissociation of areactant gas. In this manner, the carbon black particles can be producedin situ via dissociation reactions of gaseous hydrocarbons, therebyeliminating the need to feed the particles into the reactor. Sulfurparticles produced from dissociation of hydrogen sulfide are alsosuitable for use as heat absorbing particles.

The radiation absorbing particles must be dispersed in the reactorapparatus, and the form of dispersion is important. The particles shouldflow as a dust or particle cloud through the apparatus, dispersed in adispersing process gas. The radiation absorbing particles should have afine primary particle size, preferably in the sub-micron size range, andbe non-agglomerated, thus providing the highest surface area possiblefor solar radiation absorption. The heat absorbing particles may beprovided as a result of the dissociation reaction. For example, carbonblack particles can be produced in situ via dissociation reactions ofgaseous hydrocarbons. The particles produced via reactions 1-5 using themethods of the disclosure typically have a primary particle size lessthan about 50 nm and are essentially amorphous. Carbon black particlesproduced using the methods of the disclosure are essentially ash-freeand may be more amorphous than those produced using other commerciallyavailable carbon black producing processes. The particles may also beprovided by feeding the particles into the reactor.

When the particles are provided by feeding preformed particles into thereactor, several different methods can be used to disperse theparticles. The particles can be dispersed mechanically, such as byshearing on the surface of a rotating drum or brush. Alternatively, theparticles can be dispersed using the shear provided by high velocity gasexiting with the particles from a feed injection tube. Experience hasshown that the exiting “tip speed” from the injection tube should be atleast 10 m/s to provide the shear necessary for complete dispersion offine powders. Particles generated in-situ are inherently well dispersedin the process.

The process gas used for dispersing the particles must be compatiblewith the reaction process or easily separated after processing. It maybe a mixture of recycle gases from the process. Preferred dispersingprocess gases comprise natural gas, CxHy, CH4, or H2, or a combinationthereof.

In general, the radiation absorbing particles flow co-currently with theflowing gas stream through a reaction shell to maximize heat transferfrom the particles to the gas. The shell may be oriented horizontally orvertically. For the case of a vertical reaction shell process, the flowdirection may be upward or downward. Upward flow guarantees thataggregated particles will not be carried through the reaction shell, anddownward flow reduces the potential for plugging in the solids feedline. A preferred flow direction is downward with particles generatedinternally and separated downstream.

The second gas stream used to provide the “fluid-wall” blanket gasflowing inward from the porous “reaction” shell wall is preferably anon-dissociating gas so as not to plug the pores of the porous wall. Thefluid-wall gas is also selected to be compatible with the reactants andthe products, i.e., so that it will not interfere with the reaction orbe difficult to separate from the gas stream exiting the reaction shell.The fluid wall gas is preferentially a product of the reaction beingcarried out. Hydrogen (H2) is a preferred fluid wall gas when carryingout reactions (1) through (5). The H2 may be recycled from a downstreampurification process. Inert gases, such as N2 or argon are also suitablefor use as the second gas stream.

In reactors having a first and second inner shell and an outer shell, athird gas stream comprising a non-oxidizing and non-dissociating “purge”gas flows between the outermost “transparent or semi-transparentprotection” shell and the solid “heating” shell. This “purge” gas can bean hydrogen or an inert gas such as N2 or argon.

In the methods of the disclosure, heat absorbing particles are heated atleast in part with a source of concentrated sunlight (91). The reactorsmay be heated by solar energy alone or by a combination of solar energyand resistance heating of one of the shells of the reactor. The sourceof concentrated sunlight (91) may be a solar concentrator (50), as shownin FIGS. 2 and 3. These two figures also show unconcentrated sunlight(90) entering the solar concentrator. Preferably, the solar concentratorof the apparatus is designed to optimize the amount of solar thermalheating for the process. Solar fluxes between about 1500 and about 2000kW/m2 have been shown to be sufficient to heat the particles totemperatures between 1675 and 1875 K. More preferably, solar fluxesbetween about 2000 and 5000 kW/m2 are desired to achieve even highertemperatures and reactor throughputs. Most preferably, reactiontemperatures are approximately 2100 K.

The sunlight can be provided in the form of a collimated beam (spot)source, a concentric annular source distributed circumferentially aroundthe reactor, or in the form of a linearized slot source providingheating axially along the length of reactor. The light can be redirectedand focused or defocused with various optical components to provide theconcentration on or in the reactor as required. An example of a suitablesolar concentrator for use in the present disclosure is the High-FluxSolar Furnace (HFSF) at the National Renewable Energy Laboratory (NREL)in Golden, Colo. The HFSF uses a series of mirrors that concentratesunlight to an intensified focused beam at power levels of 10 kW into anapproximate diameter of 10 cm. The HFSF is described in Lewandowski,Bingham, O'Gallagher, Winston and Sagie, “Performance characterizationof the SERI Hi-Flux Solar Furnace,” Solar Energy Materials 24 (1991),550 563. The furnace design is described starting at page 551, whereinit is stated, The performance objectives set for the HFSF resulted in aunique design. To enable support of varied research objectives,designers made the HFSF capable of achieving extremely high fluxconcentrations in a two-stage configuration and of generating a widerange of flux concentrations. A stationary focal point was mandatorybecause of the nature of many anticipated experiments. It was alsodesirable to move the focal point off axis. An off-axis system wouldallow for considerable flexibility in size and bulk of experiments andwould eliminate blockage and consequent reduction in power. Inparticular, achieving high flux concentration in a two-stageconfiguration (an imaging primary in conjunction with a nonimagingsecondary concentrator) dictates a longer f/D [ratio of focal length todiameter] for the primary [concentrator] than for typical single-stagefurnaces. Typical dish concentrators used in almost all existing solarfurnaces are about f/D=0.6. To effectively achieve high fluxconcentration, a two-stage system must have an f/D=2. Values higher thanthis will not achieve significantly higher concentration due toincreased losses in the secondary concentrator. Values lower than thiswill result in a reduction of maximum achievable two-stage flux. At lowvalues of f/D, the single stage peak flux can be quite high, but theflux profiles are also very peaked and the average flux is relativelylow. With a longer f/D, two-stage system, the average flux can beconsiderably higher than in any single-stage system. The final design ofthe HFSF has an effective f/D of 1.85. At this f/D, it was also possibleto move the focal point considerably off axis (about 30 degrees) withvery little degradation in system performance. This was because of thelonger f/D and partly because of the multi-faceted design of the primaryconcentrator. This off-axis angle allows the focal point and a largearea around it to be completely removed from the beam between theheliostat and the primary concentrator.

When the outer shell is wholly transparent or has a window which extendscompletely around the shell, the concentrated sunlight is preferablydistributed circumferentially around the reactor using at least onesecondary concentrator. Depending upon the length of the reaction shell,multiple secondary concentrators may be stacked along the entire lengthof the reaction shell. For the HFSF described above, a secondaryconcentrator that is capable of delivering 7.4 kW of the 10 kW available(74% efficiency) circumferentially around a 2.54 cm diameter times 9.4cm long reaction tube has been designed, constructed, and interfaced tothe reactor.

The disclosure also provides reactor systems which combine the reactorof the disclosure with one or more other system elements. Systemelements useful for use in the present disclosure include, but are notlimited to, particle dispersion and feeding devices, sources ofconcentrated solar energy, cooling zones, filtering devices, variouspurification devices, hydrogen storage devices, and thermophotovoltaicdevices.

In one embodiment, a cooling zone is located downstream of the aerosoltransport reactor. The cooling zone is preferably expanded and of alarger diameter than the inner “reaction” shell. The cooling zone ispreferably a jacketed steel tube with a coolant flowing within thejacket of the tube. The function of the cooling zone is to provide alarger volume where product gases and dissociated product particles canbe cooled. The purpose of the expanded tube is twofold. First, itprovides for a reduced velocity of product gas and entrained particlesflowing through it and, hence, an increased residence time for cooling.Second, the expanded design allows for dissociated product particles tobe cooled while flowing in the gaseous space, thus, reducingthermophoretic deposition of fine particles on the cooler wall. Thisdesign reduces the tendency for dissociated product particles to depositalong the cooling zone wall.

Additionally, a system element for removing the solid dissociationproducts from the gas stream can be provided. Carbon black particles arepreferably removed from the gas stream after the gas exits the reactionchamber. The carbon black may be removed from the gas stream by suitablemethods as known in the art, such as by filtration, cyclonic separation,or a combination thereof. Some of the carbon black particles may berecycled in the process, preferably providing absorber surfaces forheating the gas. The carbon black may be sold as a product or may beused as a raw material to supply a carbon conversion fuel cell forgenerating electricity. The carbon black from the solar-thermaldissociation process is fine sized and preferably substantially free ofsulfur and ash. Hence, it is a preferred feed stock for supplying acarbon conversion fuel cell.

The system may also comprise a system element for separating hydrogenfrom non-dissociated gaseous components or otherwise purifying thehydrogen produced by the process. The product gas that is separated fromthe heat absorbing particles can be purified using a pressure swingadsorber (PSA), membrane or some other type of gas separation devicethat will separate hydrogen from non-dissociated gaseous reactants (i.e.CH4, CxHy, natural gas, etc.) or byproducts of reaction (e.g. acetylene,etc). Some of the purified hydrogen can be recycled to the process,preferably as the “fluid-wall” gas and “purge gas”. Some of the recycledhydrogen can be fed to an upstream hydrogenator to hydrogenatemercaptans that may have been added to the natural gas. The hydrogenatedmercaptans are then removed along with H2S in a molecular sieve such asan adsorption bed of zinc oxide particles. The bulk of the hydrogen willbe used in downstream processes, preferably to supply fuel cellbatteries for stationary generation of electricity or for on boardtransportation applications involving fuel cell vehicles. The purifiedhydrogen exiting the separation device (PSA or membrane) may supply ahydrogen pipeline at lower pressure or may be compressed and stored in astorage tank, such as at a service station for servicing fuel cellvehicles.

FIG. 4 illustrates one system comprising a hydrogenation and ZnO bed(70), solar-thermal fluid wall reactor (1), a cooling zone (60)immediately following the reactor, a baghouse filter (62), a lowpressure compressor (64), a pressure swing adsorber (66), and a highpressure compressor (68). The high pressure compressor can additionallybe connected to a hydrogen storage device, not shown in FIG. 4.

In another embodiment, a reactor with a transparent outer shell such asa quartz tube may be coupled to one or more thermophotovoltaic devices.Thermal radiation from the outermost inner shell of the reactor (e.g.from a graphite heating tube in a three shell reactor) which passes outthrough the transparent outer shell can be used to power thethermophotovoltaic devices. The thermophotovoltaic devices are placed inlocations not shielded by the solar concentrator.

Those of ordinary skill in the art will appreciate that startingmaterials, reactor components, reactor system components, and proceduresother than those specifically exemplified can be employed in thepractice of this disclosure without resort to undue experimentation. Theskilled artisan will be further aware of materials, methods andprocedures which are functional equivalents of the materials, methodsand procedures specifically exemplified herein. All such art-knownfunctional equivalents are intended to be encompassed by thisdisclosure.

All references cited herein are incorporated by reference herein to theextent that they are not inconsistent with the teachings herein.

EXAMPLES Example 1 Operation of a Three-Shell Reactor

In accordance with the present disclosure, a concentric three-tubeaerosol transport reactor was constructed and vertically interfaced tothe HFSF at NREL. The aerosol transport reactor consisted of an outer5.1 cm outside diameter times 4 mm thick times 24 cm long quartz“protection” tube, a central 2.4 cm outside diameter times 4 mm thicktimes 35.6 cm long graphite “heating” tube, and a 1.8 cm outsidediameter times 6 mm thick times 44 cm long graphite “reaction” tube. The“reaction” tube consisted of a 30 cm long porous graphite section with 7cm of solid graphite tube on both ends of the “reaction” tube. Theporosity of the graphite tube was 49% with a permeability of air (atstandard temperature and pressure (STP)) of 1 ft3/ft2/min. It was asunny day. A secondary concentrator delivered 7.4 kW of solar-thermalpower over a 9.4 cm length. The concentrator was positionedconcentrically around the outer quartz “protection” tube. A 99%methane/1% argon gas was fed at a rate of 4 standard liters per minute(slpm) into the top of the graphite “reaction” tube and flowed downward.Hydrogen “fluid-wall” gas was fed at a rate of 1 slpm to the annularregion between the inner “reaction” tube and the central “heating” tube.The hydrogen flowed within the annular region and through the poroussection of the “reaction” tube and exited radially inward providing afluid-wall of hydrogen along the inside “reaction” tube wall. Argon“purge” gas flowed at a rate of 2 slpm in the annular region between theouter quartz “protection” tube and the central solid graphite “heating”tube. The argon prevented oxidation of the graphite “heating” tube. Nocarbon black absorber particles were fed to the inner “reaction” tube.The temperature of the reactor as measured by a Type B thermocoupleinserted in the hot zone was 1873 K. Feed gas was flowed forapproximately 1 hour. A downstream gas chromatograph analyzed the steadystate composition of the exiting stream, after the 1 slpm “fluid-wall”hydrogen was subtracted out. A downstream flowmeter measured the gasflow rate as 3.2 slpm (after subtracting out the 1 slpm fluid-wall H2).The unreacted methane content was 30 mole % with the remaining gasessentially hydrogen. This corresponded to a conversion of 76% of thefeed methane for a residence time of approximately 0.03 seconds. Thesystem was taken off sun and allowed to cool. No dissociated carbon wasfound to be deposited anywhere along the inside wall of the “reaction”tube. The product carbon black collected downstream was analyzed byx-ray diffraction and found to be essentially amorphous carbon blackwith a primary particle size between approximately 20 and 40 nanometers.This example illustrates that the fluid-wall reactor tube preventeddeposition of reaction products within the reactor and allowedcontinuous operation.

Example 2 Operation of a Three-Shell Reactor with No “Fluid-Wall” GasFlow

The process conditions of Example 1 were repeated except that no“fluid-wall” hydrogen gas was flowed through the porous “reaction” tube.Within 8 minutes, the process was shut down due to difficultiesmaintaining feed gas flow using mass flow controllers. After cooling,the reactor was dismantled and inspected. It was found that carbon wasdeposited inside of the “reaction” tube. The carbon was analyzed byx-ray diffraction and found to contain a large graphitic content. Thiscomparative example illustrates that, without the fluid-wall, thereactor plugs and prevents continuous operation.

Example 3 Reactor Operation with Increased Fluid-Wall and Purge Gas FlowRates

The apparatus described in Example 1 was used except that the“fluid-wall” gas was changed to argon. It was fed at a rate of 4 slpmthrough the porous tube wall. In addition, the argon “purge” gas flowwas increased to 10 slpm.

Examples 4 to 12 Reactor Operation with Varying Methane Flow Rate andSolar Flux

The apparatus described in Example 1 was used with the gas flow ratesgiven in Example 3. The nonporous “heating” wall temperature wasmeasured through a hole in the trough section of the secondaryconcentrator using a pyrometer. For this apparatus, the temperature ofthe wall of the nonporous carbon tube was typically about 100-200 Khigher than the temperature inside the reaction tube. The solar flux wasvaried in order to achieve heating wall temperatures of 1716, 1773,1923, 2073, and 2140 K. Although the “fluid-wall” argon flow rate wasmaintained at 4 slpm, the methane flow rate was varied from 0.8 to 2.2slpm. All flow rates corresponded to average residence times betweenapproximately 10 and 20 milliseconds. The dissociation (conversion) ofmethane to hydrogen and carbon black was calculated from the measuredconcentration of H2 and is reported in Table 1.

TABLE 1 (Examples 4 to 12) Methane Dissociation Heating Wall InitialMethane Conversion of Temperature (K.) Flow Rate (slpm) Methane (%) 17160.8  0 +− 5 1716 2.2  0 +− 5 1773 1 15 +− 5 1773 2 18 +− 5 1923 1.5 29+− 5 2073 1 69 +− 5 2073 2 55 +− 5 2140 0.8 81 +− 5 2140 2.2 83 +− 5

This set of examples indicates that increasing the solar flux, which inturn increases the heating wall temperature and the temperature insidethe reactor tube, results in an increase in the thermal dissociation(conversion) of methane to H2 and carbon black. The product carbon blackfor all runs was analyzed by x-ray diffraction and transmission electronmicroscope images to determine that it was amorphous carbon black with aprimary particle size of 20 to 40 nanometers.

Examples 13 to 24 Dry Reforming with Varying Total Feed Rate and SolarFlux

The apparatus described in Example 1 was used. During these experiments,the argon “purge gas” was fed at a rate of 10 slpm. The “fluid-wall”argon was fed at a rate of 4 slpm. The reactant gas was maintained at atwo to one CH4 to CO2 feed ratio. Total flow rates of 1 and 2 slpm wereused. By changing the solar flux, the heating wall temperature wasvaried from 1873 to 2123 K, with increments of 50 K. The conversion ofmethane was calculated from the measured concentration of H2, and theconversion of CO2 was calculated from the measured concentration of CO.Both values are reported in Table 2.

TABLE 2 Examples 13 to 24 (Dry Reforming and Dissociation) Total FlowRate CH4 CO2 Heating Wall of CH4 and CO2 Conversion ConversionTemperature (K.) (slpm) (%) (%) 1873 1  35 +− 14 17 +− 11 1925 1 47 +− 122 +− 2  1977 1 58 +− 1 35 +− 5  2025 1 65 +− 7 51 +− 18 2074 1 71 +− 665 +− 7  2108 1 69 +− 5 56 +− 16 1924 2 29 +− 5 19 +− 9  1924 2 20 +− 46 +− 3 1974 2 27 +− 2 8 +− 3 2022 2 39 +− 3 15 +− 3  1801 2 51 +− 7 30+− 13 1831 2 55 +− 9 35 +− 16

The average residence time of all runs was approximately 10milliseconds. This set of examples indicates that concentrated sunlightcan be used to carry out dry CO2 reforming of CH4 reactions in shortresidence times. It is also evident that both increased temperature anddecreased reactant gas flow rate result in higher conversion of CO2 toCO and CH4 to H2.

Examples 25 to 30 Reactor Operation During Dry Reforming with VaryingTotal Feed Rate and Methane to Carbon Dioxide Feed Ratio

The apparatus described in Example 1 was used with the flow ratespresented in Example 3. For a given day, the highest available solarflux level was utilized. This resulted in heating wall temperaturesranging from 2063 to 2115 K, as seen in Table 3. Total CH4 and CO2 feedrates of 1 and 2 slpm were used. Three CH4 to CO2 feed ratios wereutilized: 1 to 1, 1.5 to 1, and 2 to 1. The conversion of methane wascalculated from the measured H2 concentration, and the CO2 conversionwas calculated from the measured CO concentration. Both values for eachexperiment appear in Table 3.

TABLE 3 Examples 25 to 30 (Simultaneous Dry Reforming and Dissociation)Total Flow CH4 to CO2 Heating Wall Rate of CH4 Feed Ratio version CH4CO2 and CO2 (molar Temperature Conversion Conversion (slpm) volume) (K)(%) (%) 1 1:1 2063 64 +− 7 33 +− 7 1 1.5:1  2114 76 +− 2 64 +− 8 1 2:12108 69 +− 5  56 +− 16 2 1:1 2083 50 +− 2 20 +− 2 2 1.5:1  2115 58 +− 334 +− 6 2 2:1 2104 55 +− 9  35 +− 16

This set of experiments shows that the fluid-wall aerosol flow reactorcan be used to carry out dry CO2 reforming of CH4 reactions with variousreactant feed ratios. It also indicates that for a given total flowrate, changing the feed ratio does not significantly change theconversion of CH4 to H2 or the conversion of CO2 to CO. However, bothconversion values are increased when the total flow rate of CH4 and CO2is decreased from 2 slpm to 1 slpm.

Additional points include

The present disclosure provides a method for carrying out hightemperature thermal dissociation reactions requiring rapid-heating andshort residence times using solar energy. In particular, the presentdisclosure provides a method for carrying out high temperature thermalreactions such as dissociation of hydrocarbon containing gases andhydrogen sulfide to produce hydrogen and dry reforming of hydrocarboncontaining gases with carbon dioxide. In the methods of the disclosurewhere hydrocarbon containing gases are dissociated, fine carbon blackparticles are also produced. The methods of the disclosure reduce orprevent the produced carbon black from depositing along the inside wallof the reactor or cooling zone. The present disclosure also providessolar-thermal aerosol transport reactors and solar-thermal reactorsystems. The present disclosure also provides systems and methods forseparating the produced carbon black from the product gases, purifyingthe hydrogen produced by the dissociation reaction, and using the carbonblack and hydrogen to generate electricity.

There is an enormous environmental benefit for carrying out hightemperature dissociation reactions directly without the combustion ofcarbonaceous fuels. Thus, the present disclosure provides a continuouscost-effective, solar-based method of deriving hydrogen and fine carbonblack particles from hydrocarbon gases. The process does not result inincreased environmental damage due to burning fossil fuels.

The process of the present disclosure uses concentrated sunlight totransfer heat at extremely high rates by radiation heat transfer toinert radiation absorbing particles flowing in dilute phase in theprocess gas. The heating to the particles is generally carried outindirectly from a heated wall or series of walls which are themselvesheated indirectly or heated directly by solar-thermal radiative heating.The inside most wall (“reaction”) is at least partially fabricated of aporous refractory material with a compatible “fluid-wall” gas flowinginward, thus, providing a blanket of gas and preventing deposition ofparticles on the inside wall. The particles subsequently becomeradiators themselves and heat flowing gases by conduction, therebyproviding the energy to carry out highly endothermic gas phasedissociation reactions. The radiative coupling to heat flowing radiationabsorbing particles is beneficial because the gases to be heated arethemselves transparent to radiative heating. Preferably, the gases andthe particles flow co-currently to maximize the temperature and heatingrate of the gases. It is possible for the absorber particles to eitherbe fed into the process with the reactant gas or to be generated in-situby the reaction itself.

In an embodiment, a method for carrying out a high temperature chemicalreaction process to produce hydrogen or synthesis gas may include atleast the following the steps: a) providing a reactor comprising atleast two reactor shells, including an innermost and an outer shell,wherein the innermost shell is substantially enclosed by each of theother reactor shells, has an inlet and an outlet and is at leastpartially porous and the outer shell is nonporous and at least partiallytransparent; b) flowing a first gas stream comprising at least onereactant gas from the inlet to the outlet of the innermost shell; c)flowing a second gas stream comprising a non-dissociating gas inwardlythrough the pores of the innermost shell; d) providing heat absorbingparticles in the first gas stream; e) heating the heat absorbingparticles at least in part with a source of concentrated sunlightthrough indirect solar thermal heating; and f) transferring heat fromthe particles to the first gas stream, thereby heating the reactant gasto a sufficiently high temperature so that a desired amount ofconversion of the reactant gas occurs, thereby producing hydrogen orsynthesis gas.

The reactant gas may be a gaseous hydrocarbon, hydrogen sulfide or amixture thereof. For example, the gaseous hydrocarbon is methane,ethane, propane, butane, or a mixture thereof. Alternatively, thereactant gas maybe at least one gaseous carbon oxide including carbondioxide, carbon monoxide, or mixtures thereof. The volume concentrationof carbon dioxide in the reactant gas can be less than 50 volumepercent. The heat absorbing particles can be carbon particles, and thecarbon particles are fed into the innermost shell with the first gasstream. The temperature of the reactor is at least about 1500 K. Thesource of concentrated sunlight can have a flux of between 1500 and 5000kW/m2.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, the invention is not limitedto the details provided. There are many alternative ways of implementingthe invention. The disclosed embodiments are illustrative and notrestrictive.

1. A high temperature chemical reactor configured to conduct a reactionprocess to that produces hydrogen or synthesis gas, comprising: areactor having at least two reactor shells, including an inner shell andan outer shell, wherein the inner shell has an inlet and an outlet andthe outer shell is nonporous and substantially encloses the second innershell, and a particle inlet configured to provide heat absorbingparticles in a first gas stream flowing in the inner shell; wherein thereactor is heated at least in part by a source of concentrated sunlight,where the inner shell is heated by the concentrated sunlight, and theinner shell re-radiates from the inner wall and heats the heat absorbingparticles in the first gas stream flowing through the inner shell, andheat transfers from the heat absorbing particles to the first gasstream, thereby heating the reactants in the first gas stream to asufficiently high temperature so that the first gas stream undergoes thedesired reaction(s), thereby producing hydrogen or synthesis gas in thefirst gas stream.
 2. The high temperature chemical reactor of claim 1,further comprising: a solar concentrator designed to optimize an amountof solar thermal heating for the reaction process by providing theconcentrated sunlight to transfer heat at extremely high rates byradiation heat transfer from the inner shell to the heat absorbingparticles flowing in the first gas stream, and where the heat to theparticles comes indirectly from a heated wall or series of walls whichare themselves heated directly or indirectly by solar-thermal radiativeheating, and the particles subsequently become radiators themselves andheat flowing gases by conduction, thereby providing energy to carry outthe endothermic reactions producing the hydrogen or synthesis gas. 3.The high temperature chemical reactor of claim 1, further comprising: asolar concentrator designed to optimize an amount of solar thermalheating for the reaction process by using concentrated sunlight totransfer heat at extremely high rates by radiation heat transfer fromthe inner shell, where the length of the inner shell and amount of fluxprovided by the solar concentrator are designed to carry out hightemperature thermal dissociation reactions requiring rapid-heating andshort residence times using solar energy, where the residence time isbetween about 1 and about 50 milliseconds, and the solar fluxes arebetween about 1500 and 5000 kW/m².
 4. The high temperature chemicalreactor of claim 1, where the concentrated solar-thermal radiationpasses through the outer shell and directly heats a second inner heatingshell, where the heating shell re-radiates from its inner wall and heatsthe inner shell where the reaction takes place within, and thus, theinner shell is heated indirectly by concentrated sunlight from thesurrounding second inner heating shell.
 5. The high temperature chemicalreactor of claim 1, where the concentrated solar-thermal radiationpasses through the outer shell and directly heats inner shell where thereaction takes place within and the inner shell re-radiates from aninner wall to heat the heat absorbing particles and the first gas streamflowing through the inner shell.
 6. The high temperature chemicalreactor of claim 1, further comprising: a cooling zone locateddownstream of the inner shell of the reactor, where the cooling zone isexpanded and of a larger diameter than the inner shell and the coolingzone provides a larger volume where product gases and dissociatedproduct particles can be cooled; and a system element for removing thesolid dissociation products from the first gas stream after the firstgas stream exits the inner shell, where the solid dissociation productsare removed from the first gas stream by 1) filtration, 2) cyclonicseparation, or 3) a combination thereof; and a low pressure compressoris connected downstream of the inner shell of the reactor.
 7. The hightemperature chemical reactor of claim 6, further comprising: a highpressure compressor is connected downstream of the inner shell of thereactor which supplies the product hydrogen based gases to a storagedevice; and a Zinc oxide bed to further purify the product hydrogenbased gases coming out of the reactor.
 8. The high temperature chemicalreactor of claim 1, further comprising: where the at least two reactorshells are vertically orientated and arranged to provide downward flowof the first gas stream with the heat absorbing particles, which reducesa potential for plugging in a particles feed line, and an interior ofthe inner shell defines a reaction chamber within which the hightemperature reaction takes place, where the inner shell is designed tobe capable of emitting sufficient radiant energy to raise thetemperature of the reactant gas(es) within the reaction chamber to alevel required to initiate and sustain the desired chemical reaction,and the inner shell is made of a high temperature refractory material,and where the refractory material subsequently heats flowing heatabsorbing particles flowing through the first inner shell and issubstantially chemically unreactive with 1) the particles, 2) thereactant gases, or the 3) product gases and 4) any combination.
 9. Thehigh temperature chemical reactor of claim 8, where the high temperaturerefractory material for the inner shell is graphite.
 10. The hightemperature chemical reactor of claim 1, wherein the reactor is heatedat least in part by the concentrated sunlight, and a second inner shellis made of graphite, and configured to have an electrical current runfrom one end of the tube to the other to generate additional heat forthe process through resistance heating of the tube.
 11. The hightemperature chemical reactor of claim 1, wherein the outer shell is atleast in part transparent or semi-transparent to pass the concentratedsunlight to flow through and heat the inner shell of the reactor, andthe outer shell is made of a high temperature material that is oxidationresistant, and the shell wall transparent area, which allows forconcentrated sunlight entry and subsequent solar thermal heating, isdesigned and selected to provide heating to meet a desired reactionresidence time requirements for the process between about 1 and about 50milliseconds.
 12. The high temperature chemical reactor of claim 1,further comprising: where the first gas stream comprises at least onereactant selected from CH4, C2H6, C3H8, CxHy where X and Y are wholenumbers, H2S, natural gas, or any combination thereof, and the first gasstream contains substantial amounts of carbon based biogases.
 13. Thehigh temperature chemical reactor of claim 1, further comprising: wherethe heat-absorbing particles are carbon based, and are indirectly heatedby radiation from a heated wall of the inner shell, that is itselfheated indirectly or directly by solar-radiation, and the radiationabsorbing particles have a fine primary particle size, preferably in thesub-micron size range, and are non-agglomerated, to provide a highsurface area possible for radiation absorption.
 14. A method ofconducting a high temperature chemical reaction that produces hydrogenor synthesis gas, comprising: conducting the high temperature chemicalreaction in a reactor having at least two reactor shells, including aninner shell and an outer shell, wherein the inner shell has an inlet andan outlet and the outer shell is nonporous and substantially enclosesthe second inner shell, and providing heat absorbing particles in afirst gas stream flowing in the inner shell; and heating the reactor atleast in part by a source of concentrated sunlight, where the innershell is heated by the concentrated sunlight, and the inner shellre-radiates from the inner wall and heats the heat absorbing particlesin the first gas stream flowing through the inner shell, and heattransfers from the heat absorbing particles to the first gas stream,thereby heating the reactants in the first gas stream to a sufficientlyhigh temperature so that the first gas stream undergoes the desiredreaction(s), thereby producing hydrogen or synthesis gas in the firstgas stream.
 15. The method of claim 14, further comprising: providingconcentrated sunlight to optimize an amount of solar thermal heating forthe reaction process to transfer heat at extremely high rates byradiation heat transfer from the inner shell to the heat absorbingparticles flowing in the first gas stream, and where the heat to theparticles comes indirectly from a heated wall or series of walls whichare themselves heated directly or indirectly by solar-thermal radiativeheating, and the particles subsequently become radiators themselves andheat flowing gases by conduction, thereby providing energy to carry outthe endothermic reactions producing the hydrogen or synthesis gas.